Is 12vdc compressor from solar possible

[tbone1004]

@2airishuman splash lube compressors can typically go down to about 2/3's of nameplate RPM before it's an issue. The Junior is spec'd to run between 1500 and 2300rpm depending on power availability. 1500 for 2hp 110v motor, 2100 for 3hp 220v motors, and 2300 for the 6hp gas motor.

The big issue I have with trying to run off of the 12vdc system is how horrible inefficient it is going to be as I laid out above. Total efficiency of the system is around 50% by the time you take 12vdc to 110vac, then run the single phase motor.
If you can run it straight off of vdc then you are at 90% efficiency, but finding a 2hp 12vdc motor is going to be hard, if not impossible. I reached out to my motor supplier for work and they said they did not have any motors from any of their suppliers in 12vdc greater than 1hp. Even if you found one, it's going to pull around 150a, so you have to keep it really close to the battery packs and run with some serious wiring.

If you have a higher voltage system, much easier, if you have a big inverter already and can deal with the inefficiency, not an issue, but when we are talking about solar systems, the difference between 50% and 90% efficiency is substantial.

 

[kelemvor]

The current solar panels I've seen don't generate enough power for that kind of application to run direct. 100w panels are usually around 2'x4'. It would have to be an awful big yacht to have sufficient room for all the necessary panels. I mean, there might be enough space on the Octopus. Maybe.

If you ran it at 240v you'd only need about 50 panels. 400sf + some spacing. I guess that's not THAT big. Maybe it is doable?

 

[2airishuman]

Modern inverters are 90% efficient, typically.

Here's a place that has a 2hp motor in 12 volts. - DC Motor Minnesota | Permanent Magnet DC Motors in Wisconsin

Large electric motors on boats are not uncommon. The anchor windlass is usually around 100 amps, and bow thrusters run well into the hundreds of amps, both at 12 volts. You run 4/0 copper if you have to, and use care with the terminations.

Also, larger inverters are common up to around 3000 watts at 12 volts, 4000 watts or more at 24 volts, with attendant amp draw.

 

[2airishuman]

The current solar panels I've seen don't generate enough power for that kind of application to run direct. 100w panels are usually around 2'x4'. It would have to be an awful big yacht to have sufficient room for all the necessary panels. I mean, there might be enough space on the Octopus. Maybe.

If you ran it at 240v you'd only need about 50 panels. 400sf + some spacing. I guess that's not THAT big. Maybe it is doable?

The idea is that you use a battery.

I get 54 cf per kwh from the compressor in my garage. So if you had, say, 5kwh of battery power, you could fill 3 or 4 cylinders (80s +/- not completely empty) at a go. Round numbers, you get 5 watts of charging in a typical day from 1 watt rated capacity of panels, so with 1 kw of panels you could dive every day.

3 panels, 40x60" each, would easily fit on the stern arch of a mono or anywhere on a cat, gives you 1kw.

LG NeON R 350W Solar Panel Fixed Frame - e Marine Systems

 

[tbone1004]

@2airishuman I checked a few of the big inverter manufacturers and it was 87% at peak efficiency, 82% at full load on average.

any idea where to find specs on those motors?

 

[2airishuman]

@2airishuman I checked a few of the big inverter manufacturers and it was 87% at peak efficiency, 82% at full load on average.

https://www.solar-electric.com/lib/wind-sun/Magnum-RD.pdf

The pure sine ones tend to be somewhat less than 90%, modified sine somewhat more.

any idea where to find specs on those motors?

I think it would take a phone call.

There's a much better selection in 24v, and specs are widely available, e.g.:

109106.00 LEESON 2HP 24VDC MOTOR C4D18FK6

I've been looking at cruising sailboats and if I ever have the opportunity to get one I'll think seriously about a 24v refit, anyway, because it makes things much easier for the alternator, inverter/charger, windlass, and bow thruster. A dive compressor would be one more reason to do it. Most newer LED lighting and electronics manufactured for the marine market will adapt to either 12v or 24v, any incandescent bulbs can be swapped, and the battery bank can be rewired, so it's just the inverter and motors and generators that have to be replaced.

 

[tbone1004]

@2airishuman on the windlass motors, I imagine they're more similar to the motors used in winches since that's essentially what they are. Those are small, super high RPM motors that are geared down to give them enough torque to actually pull significant weight. Not suitable for a compressor application because they wouldn't be able to generate enough torque to turn the compressor.
Bow thruster motors would be more appropriate and may be the right answer, didn't think about those but checked and there are some 1.5kw motors out there. If you are willing to find out who actually makes those motors it may be an option.

Even if you do a 24v refit, all of the "normal" 12v stuff we have here is 24v in many parts of the world, but bucking down to 12v is easy and efficient if you wanted to. Much easier to buck voltage than boost

 

[clownfishsydney]

I was hoping to overcome the start with a capacitor or maybe even a clutch or worst case a hand crank .

When yours draws 2.2kW is that the maximum draw... i.e. just before shut down @ 3000psi ?
How long does it take to fill an 80cf tank ?

2.2kW is workable if it takes 20min to fill 80cf to 3000psi

My dodgy maths would make this (20min = 1/3hr) roughly 1/3hr x 2.2kW = approx. 0.75kWh

If I only fill to 2000psi that should be 0.75kWh x 0.5 = 0.375kWh or 1 x 300Wh solar panel for 2 hours

I should clarify that we have a Bauer Junior II compressor, have had it for 17+ years and done over 4,500 fills.

The petrol motor is actually slightly quicker to fill a tank than the 240v electric one. It takes both of them about 18 minutes to fill from 80 bar to 220 bar for a 11 litre tank (90cf).

The maximum draw is at start up, I presume that the draw when filling is a constant 2.2kW.

On my yacht, the biggest constant load on the 12v system is probably the anchor winch (not really checked when it has been running) but you always have the engines both on when using, so not drawing from batteries. The other thing that really uses power is the microwave. We only use for very short periods, a few minutes at the most, to reheat food. It uses over 110 amps and would quickly flatten even our 750 ah battery bank and 520 watts of solar. The compressor would also use huge amounts.

Our cat is 11.3 metres (38 foot) and while it has lots of storage space, the only spot I could store the compressor is in the saloon under the table. Caused no problems there over more than 12 months of sailing the Great Barrier Reef. By a small compressor (there are smaller ones that the Junior II) and run on petrol, easy, simple.

 

[JamesBon92007]

I've had some good luck with cheap Chinese compressors .

Oops, I meant "generators"

 

[АлександрД]

My math says I should be able to do it with around 0.6kWh of power which I can make with solar.

Check this message here Early Air Fills?
Cornelius compressor.
This ours analog КПВ-1Б had powering of 27 VDC, and 340 W of the power consumption...